Simplify the following expression: $n = \dfrac{10}{5r + 2} \div \dfrac{4}{9r}$
Solution: Dividing by an expression is the same as multiplying by its inverse. $n = \dfrac{10}{5r + 2} \times \dfrac{9r}{4}$ When multiplying fractions, we multiply the numerators and the denominators. $n = \dfrac{ 10 \times 9r } { (5r + 2) \times 4}$ $n = \dfrac{90r}{20r + 8}$ Simplify: $n = \dfrac{45r}{10r + 4}$